Birthday Paradox Calculator

Birthday paradox calculator calculates the probability of two people sharing the same birthday in a group of people.

Birthday paradox is an interesting theory that most people think we need a big group of people to share the same birthday in the group.

We might need people equal to half of the year, 182 people in a group to have a 50% chance to share the same birthday since there are 365 days in a year.

However, the fact is there is a 50% chance for two people sharing the same birthday as low as 23 people. If there are 50 people in a group, the probability will rise to 97%.
That is why it is called the birthday paradox.

Birthday Paradox Formula

To calculate the birthday paradox,
first, we need to figure out the probability that the people do not share the same birthday:

P = (365)365 x (365-1)365x(365-2)365... x (365-(N-1))365
N = number of people in the group

and then by using the formula:
Birthday Paradox Probability = 1-P(not shared birthday).